Web Server Design Week 16 Old Dominion University Department of Computer Science CS 495/595 Spring 2006 Michael L. Nelson <mln@cs.odu.edu> 4/24/06
Common Gateway Interface A method for remotely invoking executable programs on a server A long-time convention http://hoohoo.ncsa.uiuc.edu/cgi/ finally defined in RFC 3875 foo.cgi GET /foo.cgi HTTP/1.1 client server 200 OK
CGI Invocation How Apache does it: http://httpd.apache.org/docs/2.0/mod/mod_cgi.html We’ll live slightly more dangerously: any executable (non-directory) file can be invoked as CGI with: POST GET w/ query string e.g. /a/b/c.cgi?var1=foo&var2=bar
CGI Operation The CGI program is responsible for returning (on STDOUT) some combination of its own headers: Content-type Location Status and other locally-defined headers Script-returned headers are: collected by the server processed; e.g.: “Location” -> HTTP/1.1 302 Found Status -> HTTP response code line combined with the server’s headers Resulting headers are returned to the client
Status % more status.cgi #!/usr/bin/perl print "Status: 678 This is not a real HTTP status code\n\n"; % telnet www.cs.odu.edu 80 Trying 128.82.4.2... Connected to xenon.cs.odu.edu. Escape character is '^]'. GET /~mln/teaching/cs595-s06/cgi/status.cgi HTTP/1.1 Host: www.cs.odu.edu HTTP/1.1 678 This is not a real HTTP status code Date: Mon, 24 Apr 2006 14:37:14 GMT Server: Apache/2 Content-Length: 0 Content-Type: text/plain Connection closed by foreign host.
Location % more location.cgi #!/usr/bin/perl print "Location: http://www.cs.odu.edu/~mln/\n\n"; % telnet www.cs.odu.edu 80 Trying 128.82.4.2... Connected to xenon.cs.odu.edu. Escape character is '^]'. GET /~mln/teaching/cs595-s06/cgi/location.cgi HTTP/1.1 Host: www.cs.odu.edu HTTP/1.1 302 Found Date: Mon, 24 Apr 2006 14:40:31 GMT Server: Apache/2 Location: http://www.cs.odu.edu/~mln/ Content-Length: 277 Content-Type: text/html; charset=iso-8859-1 <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> <html><head> <title>302 Found</title> </head><body> <h1>Found</h1> <p>The document has moved <a href="http://www.cs.odu.edu/~mln/">here</a>.</p> <hr> <address>Apache/2 Server at www.cs.odu.edu Port 80</address> </body></html>
CGI Environment Section 4.1, RFC 3875 In practice, slightly different: AUTH_TYPE, CONTENT_LENGTH, CONTENT_TYPE, GATEWAY_INTERFACE, PATH_INFO, PATH_TRANSLATED, QUERY_STRING, REMOTE_ADDR, REMOTE_HOST, REMOTE_IDENT, REMOTE_USER, REQUEST_METHOD, SCRIPT_NAME, SERVER_NAME, SERVER_PORT, SERVER_PROTOCOL, SERVER_SOFTWARE In practice, slightly different: http://www.cs.odu.edu/~mln/teaching/cs595-s06/cgi/env.cgi
How to Customize the Environment? fork() & execve() Perl: set %ENV fork() & exec() Python: fork () & execve() Others??? please share w/ the list
ENV & CGI Examples {GET, POST} X {multipart/form-data, #!/usr/bin/perl print "Content-type: text/html\n\n"; foreach $key (keys (%ENV)) { print "$key = $ENV{$key} <br>\n"; } while (<STDIN>) { print "$_<br>\n"; {GET, POST} X {multipart/form-data, application/x-form-www-urlencoded} http://www.cs.odu.edu/~mln/teaching/cs595-s06/cgi/
Advanced Topics: “Soft 404s” foo.edu/lookup.php?key=123456 what http status code do you return if: script “lookup.php” exists and has no syntax errors but key 123456 is deleted or invalid Semantic events: http - 200 database - bad key reading: “Sic Transit Gloria Telae: Towards an Understanding of the Web’s Decay” http://www2004.org/proceedings/docs/1p328.pdf